In this chapter many experimental conditions in relation to feeding have been discussed and advantages/disadvantages for animal welfare have been evaluated. What implications do they have for research on animals with regard to the animals welfare and the standardisation of experimental results?

Providing animals with food that fulfils their species-specific nutrient needs is a necessary item for securing basal welfare and reliable experimental results. However, in what way we need to provide the food in order to maintain or increase animal welfare is an important question. Is it enough to fulfil essential nutrient needs, or do we need to do more? Is it important for the animal to have the possibility to select from various food items, i.e. have more influence on composing the diets themselves? When rats were offered various diets differing in macronutrient composition, their preference varied with the time of the night. This is an indication that the needs may vary during the circadian cycle. More investigations are needed to solve whether self-selection of food is important for animal health and welfare. Whether it is important for the animals’ well-being to work for obtaining food, remains a subject of debate. When given the choice, domesticated chickens clearly show a lower preference for obtaining food by working for it as compared to their wild ancestors. However, the percentage of food obtained by working is still 30%. Results from preference tests with rats give the same result. This indicates that animals in captivity still like to work for food, at least to a certain extent. The method that can be used to make animals work for food will depend on the species-specific behaviour and needs. In case a method is chosen, it is not certain that it will remain satisfactory as it can quickly loose its novelty value as was shown in the example where rats initially had to increase their efforts for obtaining food through narrowed distance between food hopper bars.

As ad libitum feeding in long-term toxicity studies have been clearly associated with negative health effects, restricted feeding is advised. How and when to feed is important for the animals' welfare, as e.g. the frequency of stereotyped behaviour in rabbits is increased when they are fed ad libitum or restrictedly at an “unnatural” time point of day as compared to restricted feeding at a “natural” time point (just before the dark phase). Stereotyped behaviour will induce increased variation in results, as the degree of behaviour will vary for each individual and thereby the effects on energy utilisation. We believe that an adaptation of feeding schedules to the normal circadian patterns will contribute positively to welfare as well as standardisation of results. Feeding at “unnatural” times will cause wider fluctuation and perturbed physiology and will bring animals out of homeostasis, thereby decreasing welfare. Although group housing of social species is preferred over individual housing, it may be unpractical (e.g.

catheterized animals, aggressive males) and a source of unwanted extra variance. Dependent on the species, sex, experimental goals, etc. groups should be composed and monitored carefully, as group composition and behaviour can compromise standardisation and welfare.

Whether variation in food items provided is an essential factor to increase welfare is a matter of debate. Providing this dietary variation may be in conflict with the striving for standardisation of results, as the choice of individuals may be different. Also the choice of individuals during the circadian cycle may vary, contributing to a higher variation in experimental results. An indirect indication of how animals subjectively value the provision of food variation is obtained in preference testing, also involving the level of effort animals are willing to invest for obtaining this goal. By evaluating the level of investment an animal is willing to give, an indication of the motivation to reach a certain goal can be obtained.

Trying to improve welfare and fulfilling the animals' needs for a good welfare may give a potential conflict with trying to standardise experiments and reducing variation in results. On the other hand, an improved welfare may also lead to an animal that is more in balance physiologically and psychologically, thereby resulting in reduced variation as it can cope better with environmental challenges. This will depend on the circumstances and parameters measured. By carefully monitoring the animals' species-specific physiology and behaviour in experimental studies exploring the relation between nutritional factors, welfare and variation in results, more insight into these factors can be obtained.

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